1. Field of the Invention
The present invention relates to an overlaid lead giant magnetoresistive head with side reading reduction and, more particularly, to such a head wherein first and second side surfaces of a spin valve sensor are notched and replaced with refill layers for minimizing a magnetoresistive coefficient of the spin valve sensor in side regions beyond a track width of the read head.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm urges the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
An exemplary high performance giant magnetoresistive (GMR) read head employs a spin valve sensor for sensing the magnetic field signals from the rotating magnetic disk. The sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer structure and a ferromagnetic free layer structure. An antiferromagnetic pinning layer interfaces the pinned layer structure for pinning a magnetic moment of the pinned layer structure 90xc2x0 to an air bearing surface (ABS) wherein the ABS is an exposed surface of the sensor that faces the magnetic disk. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. A magnetic moment of the free layer structure is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative magnetic field signals from a rotating magnetic disk. The quiescent position, which is parallel to the ABS, is the position of the magnetic moment of the free layer structure when the sense current is conducted through the sensor in the absence of field signals.
The thickness of the spacer layer is chosen so that shunting of the sense current and a magnetic coupling between the free and pinned layer structures are minimized. This thickness is typically less than the mean free path of electrons conducted through the sensor. With this arrangement, a portion of the conduction electrons are scattered at the interfaces of the spacer layer with the pinned and free layer structures. When the magnetic moments of the pinned and free layer structures are parallel with respect to one another scattering is minimal and when their magnetic moments are antiparallel scattering is maximized. Changes in scattering changes the resistance of the spin valve sensor as a function of cos xcex8, where xcex8 is the angle between the magnetic moments of the pinned and free layer structures. The sensitivity of the sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in the resistance of the sensor as the magnetic moment of the free layer structure rotates from a position parallel with respect to the magnetic moment of the pinned layer structure to an antiparallel position with respect thereto and R is the resistance of the sensor when the magnetic moments are parallel.
In addition to the spin valve sensor the GMR read head includes nonmagnetic electrically nonconductive first and second read gap layers and ferromagnetic first and second shield layers. The spin valve sensor is located between the first and second read gap layers and the first and second read gap layers are located between the first and second shield layers. In the construction of the read head the first shield layer is formed first followed by formation of the first read gap layer, the spin valve sensor, the second read gap layer and the second shield layer. Spin valve sensors are classified as a top or a bottom spin valve sensor depending upon whether the pinning layer is located near the bottom of the sensor close to the first read gap layer or near the top of the sensor close to the second read gap layer. Spin valve sensors are further classified as simple pinned or antiparallel pinned depending upon whether the pinned layer structure is one or more ferromagnetic layers with a unidirectional magnetic moment or a pair of ferromagnetic layers that are separated by a coupling layer with magnetic moments of the ferromagnetic layers being antiparallel respectively. Spin valve sensors are still further classified as single or dual wherein a single spin valve sensor employs only one pinned layer and a dual spin valve sensor employs two pinned layers with the free layer structure located therebetween.
In a prior art spin valve sensor first and second hard bias and lead layers interface first and second side surfaces of the spin valve sensor wherein the first and second side surfaces intersect the ABS. This type of sensor is referred to in the art as a contiguous junction type of sensor and is fully described in U.S. Pat. No. 5,018,037. Each of the first and second hard bias layers is a strong magnet which longitudinally biases the free layer so that it is magnetically stable in a single domain state. Unfortunately, a magnetic moment in each of the first and second side portions of the free layer are pinned by the first and second hard bias layers so that they do not rotate (respond) to field signals from the rotating magnetic disk. As the sensor track width dimensions grow narrower the pinned regions, which are also referred to as dead layer regions, become a larger fraction of the sensor track width. Consequently, less of the free layer in the sensor track width region is available to read the field signal.
In order to overcome the problem with the prior art contiguous junction type of sensor the contiguous junctions of the first and second hard bias layers are moved further away from the track width region and first and second conducting leads overlap the first and second hard bias layers and first and second top portions of the sensor with the spacing between the leads defining the track width of the sensor. A problem with this design is that a small portion of the sense current will still pass through the sensor layers below the conducting leads, even though the conducting leads have a much lower resistance than the spin valve sensor layers. Unfortunately, this causes the spin valve layer portions below the first and second conducting leads to be slightly active so as to have some response to field signals from the rotating magnetic disk. Since these field signals are outside the track to be read the sensor is sensing field signals from adjacent tracks which is referred to as side reading. There is a strong-felt need to overcome this side reading problem in the continuous type (overlapping leads) spin valve sensor.
The present invention minimizes the side reading problem by notching the first and second side surfaces of the spin valve sensor and disposing first and second ferromagnetic refill layers in the notches wherein the ferromagnetic refill layers magnetically couple the first and second hard bias layers to first and second side edges of the free layer. The first and second conducting leads overlap the first and second hard bias layers and the first and second ferromagnetic refill layers. The notches in the side surfaces of the spin valve sensor are sized so as to reduce the magnetoresistive coefficient dr/R of the spin valve sensor portions below the first and second conducting leads. In a first embodiment of the invention a cap layer at the top of a bottom spin valve sensor is provided with first and second recessed side surfaces which, in turn, provide the first and second notches. The first and second ferromagnetic refill layers are disposed within the notches and interface the free layer so that the free layer is thicker in the regions below the first and second leads. The magnetoresistive coefficient dr/R is lowered with the increasing free layer thickness below the conducting leads and the thicker regions are further more resistant to demagnetization.
In a second embodiment the first and second side surfaces of each of the cap layer and the free layer are recessed to provide the first and second notches. First and second copper refill layers interface first and second top surfaces of the spacer layer and the first and second ferromagnetic refill layers overlay the first and second copper refill layers. Because of the increased thickness of the spacer layer in the regions below the first and second leads the magnetoresistive coefficient dr/R has been decreased. Because of the thinness of the first and second copper refill layers the first and second ferromagnetic refill layers are still magnetically coupled to the first and second hard bias layers for longitudinally biasing the free layer.
In a third embodiment of the invention the first and second side surfaces of the cap and free layers are recessed and a portion of the first and second side surfaces of the spacer layer are recessed to provide the first and second notches. First and second ferromagnetic refill layers are disposed in the first and second notches with the first and second ferromagnetic layers being directly magnetically coupled to the first and second hard bias layers and the free layer. With this embodiment the spacer layer has first and second thin portions below the first and second leads which causes a ferromagnetic coupling field between the pinned and free layers in these regions. This pins the magnetic moment of the free layer in these regions so that it will not respond to field signals from the rotating magnetic disk.
In a fourth embodiment of the invention the first and second side surfaces of each of the cap layer, free layer and spacer layer are recessed so as to provide the first and second notches. The first and second ferromagnetic refill layers are disposed within the first and second notches and are magnetically coupled between the first and second hard bias layers and the free layer. The first and second ferromagnetic refill layers interface first and second top surface portions of the pinned layer and effectively increase its thickness in the regions below the first and second leads. The extra thick pinned layer portions in these regions cannot effectively be pinned by the pinning layer therebelow so that the magnetoresistive coefficient dr/R is minimized.
In a fifth embodiment of the present invention first and second side surfaces of the cap layer and first and second side surfaces of the pinning layer are recessed in a top spin valve sensor so as to provide the first and second notches and the first and second conductive leads are disposed within the first and second notches and overlay the first and second hard bias layers. In this embodiment the first and second ferromagnetic refill layers are not required since the first and second hard bias layers interface the first and second side surfaces of the free layer for stabilizing the free layer. In this embodiment first and second side portions of the pinned layer are no longer pinned and the magnetoresistive coefficient dr/R of the regions of the sensor below the first and second leads is minimized.
An object of the present invention is to minimize the magnetoresistive coefficient dr/R of side regions of a continuous junction spin valve sensor which are below first and second conducting leads.
Another object is to provide an overlaid lead GMR head wherein a spin valve sensor has reduced side reading.
A further object is to provide a method of making the aforementioned spin valve sensors.